This fern, like other ferns, has two stages to its life-cycle. The typical fern-like stage is the sporophyte and is very rare, being known from one site in Northern Ireland: a cave near the coast in NE Antrim. Formerly the plant was common about Killarney (whence its English name) but over-collecting by gardeners and botanists in the 19th century all but exterminated it there. The other stage is the gametophyte which is like a filamentous green alga, and appears to be commoner. It is known from a number of sites in Co Fermanagh, all found since 1993.